Conventional roofing for commercial and industrial buildings usually consists of a roof deck covered by a layer of insulation followed by a water proof membrane and an exterior surface. Many commercial buildings have flat roofs upon which a commercial roofer commonly applies roll roofing in large single sheets. Asphalt is generally applied to the surface of the roof and the roll roofing is then applied on top of the asphalt. Alternatively, the roll roofing may have a layer of asphalt on one surface which is heated to apply the roll roofing to the roof.
There are many problems involving undesirable heat transfer associated with conventional commercial roofing because the roof absorbs solar energy from the sun. As a result, the roof becomes very hot during the day, causing higher interior temperatures and resulting in higher cooling costs. Typical roofing materials such as mineral cap sheets, modified bitumen, asphalt, and gravel can absorb more than 70 percent of the solar energy that falls on them. Roofs having dark roofing materials, which tend to absorb more of the sun's solar energy, may become as hot as 88° C. (190° F.) on a sunny day. Even lighter colored roofing materials (e.g. white or green) can become as hot as 79° C. (175° F.).
Certain insulation materials and constructions have been disclosed in the past to reduce cooling costs, including using a liquid medium located on a building structure which can be cooled, such as a water jacketed enclosure. See U.S. Pat. Nos. 3,450,192 and 3,563,305 of Hay. U.S. Pat. Nos. 3,994,278 and 4,082,080 of Pittinger disclose heating and cooling systems which utilize an energy source and a fluid body as a storage medium. The fluid body is distributed over the roof of a building and includes mechanisms for regulating the temperature within the enclosed structure. In these types of systems, optimum cooling efficiency cannot be obtained and an external source is needed to obtain the cooling, which results in additional costs.
Other methods for reducing cooling costs comprise applying a reflective coating onto the roof after the roof has been installed (retrofitted coatings) which reduce the amount of solar energy that is absorbed by the roof. Reflective coatings can reflect much of the sun's heat rays and can lead to reduced interior building temperatures and reduced cooling costs. For example, white roof coatings can reflect 70% to 80% of the sun's energy. Reflective coatings may include, inter alia, elastomeric coatings, aluminum fiber coatings, acrylic and polyurethane coating systems such as Mule-Hide acrylic and polyurethane coating systems available from Better Roofing Mid Atlantic, Inc. (Jacksonville, N.C.), ceramic coatings, insulating paints such as those disclosed in U.S. Pat. No. 4,623,390 of Delmonico, metal pigment paints, and metal pigment pastes such as those disclosed in U.S. Pat. No. 5,993,523 of Keemer et al. By making the roof less absorptive of the sun's heat rays, significant cooling-energy savings can be achieved. In addition, lighter colored roofs tend to last longer. See <http://www.energy-seal.com> visited May 12, 2000.
The Environmental Protection Agency (EPA) and the Department of Energy (DOE) have organized the Energy Star® Roof Products Program which is aimed at reducing cooling costs by using cool roofing products. See <http://www.energy-seal.com> visited May 12, 2000. The EPA and the DOE have recognized the energy-saving cost benefits of using reflective coatings on roofs and are advocating their use. The Energy Star® label can be used on reflective roof products that meet the EPA's specifications for solar reflectance and reliability to help consumers identify energy-efficient products. For example, the Energy Star® label may be used on roof products for low-slope roofs (surfaces with a slope of 2:12 inches or less) that have an initial solar reflectance greater than or equal to 0.65 and that have a solar reflectance greater than or equal to 0.5 three years after installation under normal conditions. As another example, the Energy Star® label may be used on roof products for steep-slope roofs (surfaces with a slope greater than 2:12 inches) that have an initial solar reflectance greater than or equal to 0.25 and that have a solar reflectance greater than or equal to 0.15 three years after installation under normal conditions.
The solar reflectance of roofing products can vary dramatically. For example, the solar reflectance of commercial asphalt shingles is rather low. Premium white shingles have a solar reflectance of around 30%, and other colors reflect less. See
<http://eetd.lbl.gov/coolroof/asshingl.htm> visited Oct. 27, 2000. The solar reflectance of smooth bitumen roofing membrane is around 6%.
<http://EandE.LBL.gov/coolroof/membrane.htm> visited Oct. 27, 2000. The solar reflectance of new, bare galvanized steel is 61%. See
<http://EandE.LBL.gov/CoolRoof/metal.htm#metal> visited Oct. 27, 2000.
While the cost benefits of reflective coated cool roofing are documented, the cost of installing cool roofing is also an issue. Conventional commercial roll roofing is often coarse and can absorb coating that is applied to it. Such coarse roofing products require the use of significant amounts of reflective coating, which can be costly. Furthermore, conventional commercial roofing generally uses other components such as heavy glass mats, granules and finishes which add to the material and installation costs. Furthermore, conventional commercial roofs require that the coating be applied after the roof is installed, which also increases installation costs.
Thus, there is a need for an easier, more cost efficient means to apply an energy-efficient reflective surface to commercial roofs. In particular, there is a need for pre-manufactured commercial roofing material which comprises a reflective coating on its surface and is less costly to manufacture and install than conventional commercial roofing materials.